Method for manufacturing substrate for semiconductor device

ABSTRACT

A substrate for semiconductor device includes a substrate, a reaction layer provided on a back surface of the substrate, a transmission preventing metal having a transmittance with respect to red light or infrared light lower than that of the substrate and a material of the substrate being mixed in the reaction layer, and a metal thin film layer formed on a back surface of the reaction layer and formed of the same material as the transmission preventing metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. patent applicationSer. No. 14/922,403 filed Oct. 26, 2015, which claims benefit ofJapanese Patent Application No. 2015-011445 filed Jan. 23, 2015, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to, for example, a substrate for use inmaking a semiconductor device and to a method of manufacturing thesubstrate.

Background Art

Various kinds of processing are performed on a semiconductor substrateto make on the substrate a circuit having components such astransistors, resistors and capacitors. For example, a metal thin film oran insulating film is formed on a substrate by a semiconductormanufacturing apparatus and a resist is patterned by an exposureapparatus.

In a wafer process in which various kinds of processing are performed ona substrate, the presence/absence of the substrate is detected with asubstrate recognition sensor in a semiconductor manufacturing apparatus.For detection of the presence/absence of an Si or GaAs substrate, theproperty of the substrate to absorb (or reflect) red light or infraredlight is utilized. More specifically, the absence of the substrate isrecognized when red light or infrared light is incident on the sensor.Also, the presence of the substrate is recognized when red light orinfrared light is absorbed by the substrate and is not incident on thesensor.

In recent years, a compound semiconductor substrate such as an SiC orGaN substrate having a bandgap wider than that of Si has been put to usein a power device or a radiofrequency device in some cases. Since SiC orGaN is transparent to red light or infrared light, the presence/absenceof the substrate cannot be detected by means of red light or infraredlight.

Japanese Patent Laid-Open No. 2010-141124 discloses an arrangement inwhich a total reflecting surface provided on an end portion of asubstrate reflects red light or the like.

A semiconductor manufacturing apparatus used to process an Si or GaAssubstrate or the like detects the presence/absence of the substrate bymeans of red light or infrared light. If a new detection system isconstructed to detect a substrate transparent to red light or infraredlight, the manufacturing cost is increased. It is, therefore, preferableto process a substrate transparent to red light or infrared light withan existing semiconductor manufacturing apparatus capable of detectingthe presence/absence of a substrate transparent to red light or infraredlight. The technique disclosed in Japanese Patent Laid-Open No.2010-141124, however, uses a total reflecting surface provided on an endportion of a substrate and therefore has a problem of being incapable ofdetecting the presence/absence of the substrate at a central portion ofthe substrate.

A method of enabling detection of a substrate transparent to red lightor infrared light by forming a metal thin film layer such as Cr, W or Alhaving a low transmittance with respect to red light or infrared lighton the back surface of the substrate is conceivable. However, there is apossibility of the metal thin film layer being separated or etched in aprocess in which treatments such as heat treatment, dry etching, wetetching and treatment with a chemical solution are repeatedly performed.

SUMMARY OF THE INVENTION

The present invention has been achieved to solve the above-describedproblems, and an object of the present invention is to provide asubstrate for semiconductor device capable of being processed withoutany detrimental effect by a semiconductor manufacturing apparatus usingred light or infrared light for detection of the presence/absence of asubstrate, and a method of manufacturing the substrate for semiconductordevice.

The features and advantages of the present invention may be summarizedas follows.

According to one aspect of the present invention, a substrate forsemiconductor device includes a substrate, a reaction layer provided ona back surface of the substrate, a transmission preventing metal havinga transmittance with respect to red light or infrared light lower thanthat of the substrate and a material of the substrate being mixed in thereaction layer, and a metal thin film layer formed on a back surface ofthe reaction layer and formed of the same material as the transmissionpreventing metal.

According to another aspect of the present invention, a method ofmanufacturing a substrate for semiconductor device includes a step offorming on a back surface of a substrate a metal thin film layer havinga transmittance with respect to red light or infrared light lower thanthat of the substrate, and a reaction step of diffusing a material ofthe metal thin film layer into the substrate by heating the substrateand the metal thin film layer so that a reaction layer is formed inwhich a material of the substrate and the material of the metal thinfilm layer are mixed with each other.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a substrate for semiconductor device accordingto a first embodiment;

FIG. 2 is a diagram showing a method of detecting the presence/absenceof the substrate;

FIG. 3 is a front view of a substrate for semiconductor device accordingto the second embodiment;

FIG. 4 is a front view of a substrate for semiconductor device accordingto the third embodiment; and

FIG. 5 is a front view of a substrate for semiconductor device accordingto the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A substrate for semiconductor device and a method of manufacturing thesame according to an embodiment of the present invention will bedescribed with reference to the drawings. Components identical orcorresponding to each other are indicated by the same referencecharacters and repeated description of them is omitted in some cases.

First Embodiment

FIG. 1 is a front view of a substrate for semiconductor device accordingto a first embodiment of the present invention. The substrate forsemiconductor device according to the first embodiment includes asubstrate 10. The substrate 10 is formed of a material such as SiC orGaN transparent to red light or infrared light. A reaction layer 12 isprovided on a back surface of the substrate 10. The reaction layer 12 isa layer in which a transmission preventing metal having a transmittancewith respect to red light or infrared light lower than that of thesubstrate 10 and the material of the substrate 10 are mixed with eachother.

A metal thin film layer 14 is formed on a back surface of the reactionlayer 12. The metal thin film layer 14 is formed of the same material asthe aforementioned transmission preventing metal. The metal thin filmlayer 14 is formed, for example, of an alloy containing Ni or of Ni. Thealloy containing Ni is, for example, NiCr, NiFe, NiMo, NiTi or NiW.

A method of manufacturing the substrate for semiconductor deviceaccording to the first embodiment of the present invention will bedescribed. The metal thin film layer 14 having a transmittance withrespect to red light or infrared light lower than that of the substrate10 is first formed on the back surface of the substrate 10. The metalthin film layer 14 is formed, for example, by vapor deposition orsputtering.

Subsequently, a reaction step is executed. In the reaction step, thesubstrate 10 and the metal thin film layer 14 are heated to diffuse thematerial of the metal thin film layer 14 into the substrate 10, therebyforming the reaction layer 12 in which the material of the substrate 10and the material of the metal thin film layer 14 are mixed with eachother. It is preferable to heat the substrate 10 and the metal thin filmlayer 14 to a temperature equal to or higher than 850° C. by rapidthermal annealing or the like.

On the substrate thus completed, treatments such as heat treatment, dryetching, wet etching and treatment with a chemical solution for formingsemiconductor elements on the substrate are repeatedly performed. Whenhandling (transport) or alignment of the substrate for example isperformed, a place where the substrate is present or a place where thesubstrate is absent is irradiated with red light or infrared light todetect the presence/absence of the substrate. FIG. 2 is a diagramshowing a method of detecting the presence/absence of the substrate.Rays 15 which are red light or infrared light are incident on thesubstrate and are reflected by the metal thin film layer 14. In thiscase, rays 15 are not incident on a sensor 16 and it is, therefore,recognized that the substrate is present in the semiconductormanufacturing apparatus. On the other hand, when rays 15 are incident onthe sensor 16, it is recognized that the substrate is absent in thesemiconductor manufacturing apparatus.

In the case where only forming of a metal thin film layer (Cr, W or Alfor example) by vapor deposition, sputtering or chemical vapordeposition is performed, the force of adhesion of the metal thin filmlayer to the substrate is low. If the metal thin film layer is separatedor etched in a wafer process, it becomes impossible to detect thepresence/absence of the substrate and a substrate recognition erroroccurs. To prevent this, in the first embodiment of the presentinvention, a component of the metal thin film layer 14 is diffused intothe substrate 10 to form the reaction layer 12. The reaction layer 12increases the force of adhesion between the substrate 10 and the metalthin film layer 14. Separation and etching of the metal thin film layer14 can be prevented with the reaction layer 12. Consequently, thesubstrate can be processed without any detrimental effect by asemiconductor manufacturing apparatus using red light or infrared lightfor detection of the presence/absence of the substrate.

Since the substrate for semiconductor device according to the firstembodiment of the present invention has the reaction layer 12 and themetal thin film layer 14 formed on the entire back surface of thesubstrate 10, red light or infrared light may be made incident either onan end portion or on a central portion of the substrate.

The substrate for semiconductor device according to the first embodimentof the present invention is characterized by preventing separation orthe like of metal thin film layer 14 with the reaction layer 12. Variousmodifications can be made without losing this feature. For example, a(transparent) substrate or semiconductor layer may be formed on thesubstrate 10. Substrates for semiconductor device and methods ofmanufacturing the same according to embodiments described below have anumber of commonalities with the first embodiment and will therefore bedescribed mainly with respect to points of difference from the firstembodiment.

Second Embodiment

FIG. 3 is a front view of a substrate for semiconductor device accordingto the second embodiment of the present invention. This substrateincludes a semiconductor layer 20 formed on the front surface of thesubstrate 10 and an insulating film 22 formed on the front surface ofthe semiconductor layer 20. The insulating film 22 is, for example, anSiN film or an SiO film.

A method of manufacturing the substrate for semiconductor deviceaccording to the second embodiment will be described. Before thereaction step, the semiconductor layer 20 is formed on the front surfaceof the substrate 10 and the insulating film 22 is formed on the frontsurface of the semiconductor layer 20. The insulating film 22 is formedby chemical vapor deposition or sputtering. The reaction step isthereafter executed. Because the substrate is heated to a highertemperature in the reaction step, there is an apprehension ofdenaturation of the semiconductor layer 20. Denaturation of thesemiconductor layer 20, however, can be prevented with the insulatingfilm 22. Thus, even in a case where the semiconductor layer 20 is formedon the substrate 10 before the reaction step, denaturation of thesemiconductor layer 20 can be prevented by providing the insulating film22.

Third Embodiment

FIG. 4 is a front view of a substrate for semiconductor device accordingto the third embodiment of the present invention. This substrateincludes an etching protective film 30 on the back surface of the metalthin film layer 14. The etching protective film 30 is formed of SiC,HfO₂, ZnO₂ or a precious metal. The precious metal is, for example, Au,Pt or Pd. The etching protective film 30 is hard to etch in any etchingstep in a wafer process.

The etching protective film 30 is formed on the back surface of themetal thin film layer 14 by vacuum deposition, sputtering, chemicalvapor deposition or atomic layer deposition (ALD). The protective film30 may be formed either before or after the reaction step.

Etching is performed a number of times in a wafer process and there is apossibility of the metal thin film layer 14 being reduced by theetching. In the third embodiment of the present invention, therefore,the etching protective film 30 is provided on the back surface of themetal thin film layer 14. The reduction of the metal thin film layer 14by the etching can be limited with the etching protective film 30.

Fourth Embodiment

FIG. 5 is a front view of a substrate for semiconductor device accordingto the fourth embodiment of the present invention. An additional metalthin film layer 40 is formed on the back surface of the metal thin filmlayer 14. The additional metal thin film layer 40 is formed, forexample, of W, Cr or Al. The additional metal thin film layer 40 formedof W, Cr or Al has a transmittance with respect to red light or infraredlight lower than that of the metal thin film layer 14 formed of an alloycontaining Ni or of Ni. The etching protective film 30 is formed on theback surface of the additional metal thin film layer 40. The etchingprotective film 30 is formed of SiC, HfO₂, ZnO₂ or a precious metal.

A method of manufacturing the substrate for semiconductor deviceaccording to the fourth embodiment of the present invention includes astep of forming the additional metal thin film layer 40 of W, Cr or Alon the back surface of the metal thin film layer 14, and a step offorming the etching protective film 30 of SiC, HfO₂, ZnO₂ or a preciousmetal on the back surface of the additional metal thin film layer 40.These steps may be performed either before or after the reaction step.

Since the additional metal thin film layer 40 has a transmittance withrespect to red light or infrared light lower than that of the metal thinfilm layer 14, the accuracy of detection of the presence/absence of thesubstrate can be improved. The etching protective film 30 may beremoved. A suitable combination of the features of the substrates forsemiconductor device and the methods of manufacturing the same accordingto the embodiments described above may be made and used as desired.

According to the present invention, separation and etching of the metalthin film layer can be inhibited by diffusing a component of the metalthin film layer into the substrate.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. A method of manufacturing a substrate forsemiconductor device, comprising: a step of forming on a back surface ofa substrate a metal thin film layer having a transmittance with respectto red light or infrared light lower than that of the substrate; areaction step of diffusing a material of the metal thin film layer intothe substrate by heating the substrate and the metal thin film layer sothat a reaction layer is formed in which a material of the substrate andthe material of the metal thin film layer are mixed with each other; anda detection step of detecting, after the reaction step, the presence orabsence of the substrate in accordance with the presence or absence ofreflected red or infrared light from the metal thin film layer.
 2. Amethod of manufacturing a substrate for semiconductor device,comprising: a step of forming on a back surface of a substrate a metalthin film layer having a transmittance with respect to red light orinfrared light lower than that of the substrate; a reaction step ofdiffusing a material of the metal thin film layer into the substrate byheating the substrate and the metal thin film layer so that a reactionlayer is formed in which a material of the substrate and the material ofthe metal thin film layer are mixed with each other; and a step offorming a semiconductor layer on a front surface of the substrate andforming an insulating film on a front surface of the semiconductor layerbefore the reaction step.
 3. A method of manufacturing a substrate forsemiconductor device, comprising: a step of forming on a back surface ofa substrate a metal thin film layer having a transmittance with respectto red light or infrared light lower than that of the substrate; areaction step of diffusing a material of the metal thin film layer intothe substrate by heating the substrate and the metal thin film layer sothat a reaction layer is formed in which a material of the substrate andthe material of the metal thin film layer are mixed with each other; anda step of forming an etching protective film of SiC, HfO₂, ZnO₂ or aprecious metal on a back surface of the metal thin film layer.
 4. Themethod of manufacturing a substrate for semiconductor device accordingto claim 1, further comprising a step of forming an additional metalthin film layer of W, Cr or Al on a back surface of the metal thin filmlayer.
 5. The method of manufacturing a substrate for semiconductordevice according to claim 4, further comprising a step of forming anetching protective film of SiC, HfO₂, ZnO₂ or a precious metal on a backsurface of the additional metal thin film layer.
 6. The method ofmanufacturing a substrate for semiconductor device according to claim 1,wherein the metal thin film layer is formed of an alloy containing Ni orof Ni.
 7. The method of manufacturing a substrate for semiconductordevice according to claim 1, wherein the substrate is formed of SiC orGaN.
 8. The method of manufacturing a substrate for semiconductor deviceaccording to claim 1, wherein the detection step is performed whentreatments for forming semiconductor elements on the substrate areperformed.